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| Tyres
most critical part of a car |
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There
have been several reports of tyre blow-outs on the super-fast Mumbai-Pune
Expressway, some resulting in very nasty accidents. When a tyre blows
at high speed, you would be lucky to get away with anything less than
a short stay in hospital. Ask Ford or Firestone.
Driving your car to the limit on the expressway is easy but not for the
tyres which, at flat-out speeds, are subjected to tremendous forces that
can sometimes lead to tyre failure. To put it in perspective, imagine
tying a stone to one end of a long rubber cord and then twirling it round
and round, faster and faster. At one point, the centrifugal force acting
on the stone will snap the cord. Similarly, the structure of a tyre, which
is pulled outwards at very high rotational speeds, can give way.
This is why all tyres come with a ‘speed rating’, which is the
safe limit to which the car can be driven. Though most Indian cars run
with tyres with the correct speed ratings, the locally-made rubber is
designed for longevity and not performance which, to a certain extent,
limits a tyre’s high speed capability, particularly when it is not
used under optimal conditions.
In
fact, blow-outs in India usually occur not because of design or manufacturing
defects but because of badly maintained tyres. Firstly, 90 per cent of
all motorists run on improper inflation pressures, singularly the tyre’s
biggest enemy. A tyre that has lost 10psi can lose half its ability to
stop and turn. And no matter how technologically advanced or safe a car
is, tyres cannot do their job unless they are pumped up to the specified
pressure.
The other danger of low tyre pressures is excessive heat build-up. Lower
the pressure, greater the flexing in the sidewall, which produces heat.
Excessive heat doesn’t allow the tyre to maintain its physical integrity
and it comes apart or ‘blows out’. Another danger are tyres
which are more than 4-5 years old, even if they show few signs of wear.
Rubber has a limited life and a tyre’s strength deteriorates with
age, making it more prone to high-speed blow-outs.
Until now, tyre blow-outs were never an issue in India simply because
the driving environment did not allow motorists to get up to serious speeds.
But with roads like the expressway coming, drivers could be riding on
rolling time bombs. The upshot of this, if anything, is that consumers
will give new importance to the most critical part of a car that has often
been overlooked.
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March 2001 